Ultra-broadband UV microscope imaging system with wide range zoom capability

ABSTRACT

An ultra-broadband ultraviolet (UV) catadioptric imaging microscope system with wide-range zoom capability. The microscope system, which comprises a catadioptric lens group and a zooming tube lens group, has high optical resolution in the deep UV wavelengths, continuously adjustable magnification, and a high numerical aperture. The system integrates microscope modules such as objectives, tube lenses and zoom optics to reduce the number of components, and to simplify the system manufacturing process. The preferred embodiment offers excellent image quality across a very broad deep ultraviolet spectral range, combined with an all-refractive zooming tube lens. The zooming tube lens is modified to compensate for higher-order chromatic aberrations that would normally limit performance.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/681,528, filed Jul. 22, 1996 now U.S. Pat. No. 5,717,518 andentitled "Broad Spectrum Ultraviolet Catadioptric Imaging System," whichis hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to an ultra-broadband ultraviolet (UV)catadioptric imaging microscope system, and more specifically to animaging system that comprises a UV catadioptric objective lens group anda wide-range zooming tube lens group.

2. Description of the Prior Art

Catadioptric imaging systems for the deep ultraviolet spectral region(about 0.19 to 0.30 micron wavelength) are known. U.S. Pat. No.5,031,976 to Shafer and U.S. Pat. No. 5,488,229 to Elliott and Shaferdisclose two such systems. These systems employ the Schupmann achromaticlens principle and the Offner-type field lens. Axial color and primarylateral color are corrected, but not higher order lateral color. This isthe limiting aberration in these systems when a broad spectral range iscovered.

The above-noted '976 Shafer patent discloses an optical system based onthe Schupmann achromatic lens principle which produces an achromaticvirtual image. A reflective relay then creates an achromatic real imagefrom this virtual image. The system, reproduced here as FIG. 1, includesan aberration corrector group of lenses 101 for correcting imageaberrations and chromatic variation of image aberrations, a focusinglens 103 for receiving light from the group 101 and producing anintermediate image at plane 105, a field lens 107 of the same materialas the other lenses placed at the intermediate image plane 105, a thicklens 109 with a plane mirror back coating 111 whose power and positionare selected to correct the primary longitudinal color of the system inconjunction with the focusing lens 103, and a spherical mirror 113located between the intermediate image plane and the thick lens 109 forproducing a final image 115. Most of the focusing power of the system isdue to the spherical mirror 113 which has a small central hole near theintermediate image plane 105 to allow light form the intermediate imageplane 105 to pass through to the thick lens 109. The mirror coating 111on the back of the thick lens 109 also has a small central hole 119 toallow light focused by the spherical mirror 113 to pass through to thefinal image 115. While primary longitudinal (axial) color is correctedby the thick lens 109, the Offner-type field lens 107 placed at theintermediate image 105 has a positive power to correct secondarylongitudinal color. Placing the field lens slightly to one side of theintermediate image 105 corrects tertiary longitudinal color. Placing thefield lens slightly to one side of the intermediate image 105 correctstertiary longitudinal color. Thus, axial chromatic aberrations arecompletely corrected over a broad spectral range. The system alsoincidentally corrects for narrow band lateral color, but fails toprovide complete corrections of residual (secondary and higher order)lateral color over a broad UV spectrum.

The above-noted '229 patent to Elliott and Shafer provides a modifiedversion of the optical system of the '976 patent, which has beenoptimized for use in 0.193 micron wavelength high power excimer laserapplications such as ablation of a surface 121' as seen in FIG. 2. Thisprior art system has an aberration corrector group 101', focusing lens103', intermediate focus 105', field lens 107', thick lens 109', mirrorsurfaces 111' and 113' with small central opening 117' and 119' thereinand a final focus 115' as in the prior '976 patent, but repositions thefield lens 107' so that the intermediate image or focus 105' liesoutside of the field lens 107' to avoid thermal damage from the highpower densities produced by focusing the excimer laser light. Further,both mirror surfaces 111' and 113' are formed on lens elements 108' and109'. The combination of all light passing through both lens elements108' and 109' provides the same primary longitudinal color correction ofthe single thick lens 109 in FIG. 1, but with a reduction in total glassthickness. Since even fused silica begins to have absorption problems atthe very short 0.193 micron wavelength, the thickness reductions isadvantageous at this wavelength for high power levels. Though theexcimer laser source used for this optical system has a relativelynarrow spectral line width, the dispersion of silica near the 0.193micron wavelength is great enough that some color correction is stillneeded. Both prior art systems have a numerical aperture of about 0.6.

Longitudinal chromatic aberration (axial color) is an axial shift in thefocus position with wavelength. The prior art system seen in FIG. 1completely corrects for primary, secondary and tertiary axial color overa broad wavelength band in the near and deep ultraviolet (0.2 micron to0.4 micron region). Lateral color is a change in magnification or imagesize with wavelength, and is not related to axial color. The prior artsystem of FIG. 1 completely corrects for primary lateral color, but notfor residual lateral color. This is the limiting aberration in thesystem when a broad spectral range is covered.

U.S. patent application Ser. No. 08/681,528, filed Jul. 22, 1996, is fora catadioptric UV imaging system with performance improved over thesystems of the above-describe patents. This system employs anachromatized field lens group to correct for secondary and higher orderlateral color, which permits designing a high NA, large field,ultra-broadband UV imaging system.

Zooming systems in the visible wavelengths are well-known. They eitherdo not require very high levels of correction of higher-order coloreffects over a broad spectral region, or do require correction, butaccomplish this by using three or more glass types. In the deep UV,there are very few materials that can be used for chromatic aberrationcorrection, making the design of high performance, broadband opticsdifficult. It is even more difficult to correct for chromaticaberrations for ultra-broadband optics with wide-range zoom.

There remains, therefore, a need for an ultra-broadband UV microscopeimaging system with wide-range zoom capability.

SUMMARY OF THE INVENTION

The present invention has an object to provide a catadioptric imagingsystem which corrects for image aberrations, chromatic variation ofimage aberrations, longitudinal (axial) color and lateral color,including residual (secondary and higher order) lateral color correctionover an ultra-broad spectral range in the near and deep UV spectral band(0.2 to 0.4 micron).

Another object is to provide an UV imaging system, useful as amicroscope or as micro-lithography optics, with a large numericalaperture of 0.9 and with a field of view of at least one millimeter. Thesystem is preferably tele-centric.

The invention is a high performance, high numerical aperture,ultra-broad spectral region catadioptric optical system with zoomingcapability, comprising an all-refractive zooming tube lens section withone collimated conjugate, constructed so that during zooming itshigher-order chromatic aberrations (particularly higher-order lateralcolor) do not change; and a non-zooming high numerical aperturecatadioptric objective section which compensates for the uncorrected(but stationary during zoom) higher-order chromatic aberration residualsof the zooming tube lens section.

These and other objects and advantages of the present invention willbecome apparent to those skilled in the art from the following detaileddescription and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prior art system that completely corrects for primary,secondary and tertiary axial color over a broad wavelength band in thenear and deep ultraviolet (0.2 micron to 0.4 micron), but not forresidual lateral color;

FIG. 2 is a modified version of the '976 Shafer patent optimized for usein 0.193 micron wavelength high power excimer laser applications;

FIG. 3 is a schematic side view of a catadioptric imaging system inaccord with the parent application;

FIG. 4 is a schematic side view of a catadioptric imaging system inaccordance with the present invention;

FIG. 5 is schematic side view of a catadioptric imaging system in thethree positions having 36×, 64× and 100× power magnifications inaccordance with a first embodiment of the invention;

FIG. 6 is a schematic side view of a catadioptric imaging system inthree positions having 36×, 64× and 100× power magnifications inaccordance with a second embodiment of invention;

FIG. 7 is a schematic side view of a catadioptric imaging system inthree positions having 36×, 64× and 100× power magnification inaccordance with a third embodiment of the invention; and

FIG. 8 is a schematic side view of a zooming catadioptric imaging systemin an application for the inspection of semiconductor wafers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 3 shows a catadioptric imaging system of the parent invention,which is especially suited for use in broadband deep ultravioletapplications and is made up of a focusing lens group 11 for forming anintermediate image 13, a field lens group 15 disposed proximate to theintermediate image 13 for correcting chromatic aberrations, and acatadioptric group 17 for focusing light from the intermediate image 13to a final image 19. The imaging system is optimized to correct bothmonochromatic (Seidel) aberrations and chromatic aberrations(longitudinal and lateral), as well as chromatic variations of themonochromatic aberrations, over a wavelength band that extends into thedeep ultraviolet (UV) portion of the spectrum, covering 0.20 to 0.40micron UV light. The catadioptric system of the parent invention can beadapted for a number of UV imaging applications, including as a UVmicroscope objective, a collector of surface scattered UV light in awafer inspection apparatus, or as mask projection optics for a UVphotolithography system.

The focusing lens group 11 in FIG. 3 consists of seven lens elements21-27, with two of the lens elements (21 and 22) separated by asubstantial distance from the remaining five lens elements (23-27). Theseparations of the pair of lens elements 21 and 22 from the remainingfive lens elements 23-27 is typically on the order of at least one-halfthe total combined thickness of the five lens elements 23-27. Forexample, lens elements 23-27 may span a distance of about 60 millimeters(mm) and lens element 22 may be 30 to 60 mm from lens element 23. Theactual dimensions depend on the scale chosen for the embodiment. The twolenses 21 and 22 form a low power doublet for correcting chromaticvariation of monochromatic image aberrations, such as coma andastigmatism. By having this doublet 21 and 22 relatively far from theother system components, the shift of the light beam with field angleson these two lenses is maximized. That in turn helps greatly inachieving the best correction of chromatic variation of aberrations.

The five lenses 23-27 of the main focusing subgroup consist of a thickstrong negative meniscus lens 23, an opposite-facing strongly-curvednegative meniscus lens 24, a strong bi-convex lens 25, a strong positivemeniscus lens 26, and an opposite-facing strongly-curved, but very weak,meniscus lens 27 of either positive or negative power. Variations ofthis lens 23-27 subgroup are possible. The subgroup focuses the light toan intermediate image 13. The curvature and positions of the lenssurfaces are selected to minimize monochromatic aberrations and tocooperate with the doublet 21-22 to minimize chromatic variations ofthose aberrations.

The field lens group 15 typically comprises an achromatic triplet,although any achromatized lens group can be used. Both fused silica andCaF₂ glass materials are used. Other possible deep UV transparentrefractive materials can include MgF₂, SrF₂, LaF₃ and LiF glasses, ormixtures thereof. In addition to refractive materials, diffractivesurfaces can be used to correct chromatic aberrations. Because thedispersions between the two UV transmitting materials, CaF₂ glass andfused silica, are not very different in the deep ultraviolet, theindividual components of the group 15 have strong curvatures. Primarycolor aberrations are corrected mainly by the lens elements in thecatadioptric group 17 in combination with the focusing lens group 11.Achromatization of the field lens group 15 allows residual lateral colorto be completely corrected.

The catadioptric group 17 of FIG. 3 includes a fused silica meniscuslens 39 with a back surface having coating 41, and fused silica lens 43with a back surface having a reflective coating 45. The two lenselements 39 and 43 front surfaces face each other. The reflectivesurface coating 41 and 45 are typically aluminum, possibly with adielectric overcoat to enhance reflectivity.

The first lens 39 has a hole 37 centrally formed therein along theoptical axis of the system. The reflective coating 41 likewise ends atthe central hole 37 leaving a central optical aperture through whichlight can pass unobstructed by either the lens 39 or its reflectivecoating 41. The optical aperture defined by the hole 37 is in thevicinity of the intermediate image plane 13 so that there is minimumoptical loss. The achromatic field lens group 15 is positioned in ornear the hole 37. The second lens 43 does not normally have a hole, butthere is a centrally located opening or window 47 where the coating isabsent on the surface reflective coating 45. The optical aperture inlens 39 with its reflective coating 41 need not be defined by a hole 37in the lens 39, but could be defined simply by a window in the coating41 as in coating 45. In that case, light would pass one additional timethrough the refractive surfaces of lens 39.

Light from the source transmitted along the optical axis toward theintermediate image plane 13 passes through the optical aperture 37 inthe first lens 39 and then through the body of the second lens 43 whereit is reflected by the near planar (or planar) mirror coating 45 backthrough the body of the second lens 43. The light then passes throughthe first lens 39, is reflected by the mirror surface 41 and passes backthrough the first lens 39. Finally the light, now strongly convergentpasses through the body of the second lens 43 for a third time, throughthe optical aperture 47 to the target image plane adjacent aperture 47.The curvatures and positions of the first and second lens surfaces areselected to correct primary axial and lateral color in conduction withthe focal lens group 11.

For a flexible deep UV microscope system, it is important to providevarious magnifications, numerical apertures, field sizes, and colors. Inprinciple, an UV microscope system can comprise several catadioptricobjectives, tube lenses, and zoom lenses. However, several problems areencountered when designing a complete microscope system. First, themicroscope design needs to accommodate many large size catadioptricobjectives to provide different magnifications and numerical apertures.Second, in order to maintain image quality, chromatic variation ofaberrations of each tube lens must be corrected to the same degree asthe objective itself. Third, the chromatic variation of aberrations of azooming system must be corrected over the full range of zoom. Theseproblems are addressed by the present invention.

An ultra-broadband UV microscope imaging system according to the presentinvention as illustrated in FIG. 4 comprises a catadioptric objectivesection 128 and a zooming tube lens group sections 139. The catadioptricobjective section 128 comprises a catadioptric lens group 122, a fieldlens group 127, a focusing lens group 129. The beam splitter 132provides an entrance for the UV light source. The aperture stop 131 isused to adjust the system imaging numerical aperture (NA). Themicroscope system images an object 120 (e.g., a wafer being inspected)to the image plane 140. The complete 0.9 NA catadioptric objectivesection 128 is also described in the parent patent application.

The catadioptric objective section 128 is optimized for ultra-broadbandimaging in the UV spectral region (about 0.20 to 0.40 micronwavelength). It has excellent performance for high numerical aperturesand large object fields. This invention uses the Schupmann principle incombination with an Offner field lens to correct for axial color andfirst order lateral color, and an achromatized field lens group tocorrect the higher order lateral color. The elimination of the residualhigher order chromatic aberrations makes the ultra-broadband UVobjective design possible.

The catadioptric lens group 122 includes a near planar or planarreflector 123, which is a reflectively coated lens element, a meniscuslens 125, and a concave spherical reflector. Compared to thereflectively coated lens element 39 in FIG. 3, the preferred embodimentuses a concave reflector 124 and a large meniscus lens 125 to simplifymanufacturing. Both reflective elements have central optical apertureswithout reflective material to allow light from the intermediate imageplane 126 to pass through the concave reflector, be reflected by thenear planar (or planar) reflector 123 onto the concave reflector 124,and pass back through the near planar (or planar) reflector 123,traversing the associated lens element or elements on the way.

The achromatic multi-element field lens group 127 is made from two ormore different refractive materials, such as fused silica and fluorideglass, or diffractive surfaces. The field lens group 127 may beoptically coupled together or alternatively may be spaced slightly apartin air. Because fused silica and fluoride glass do not differsubstantially in dispersion in the deep ultraviolet range, theindividual powers of the several component element of the field lensgroup need to be of high magnitude. Use of such an achromatic field lensallows the complete correction of axial color and lateral color over anultra-broad spectral range. In the simplest version of the design, onlyone field lens component need be of a refractive material different thanthe other lenses of the system. Compared to group 15 in FIG. 3, thefield lens group 127 is moved slightly from the intermediate imagelocation to reduce the heat load and surface scattering of the fieldlens group.

The present invention has a focusing lens group 129 with multiple lenselements, preferably all formed from a single type of material, withrefractive surfaces having curvatures and positions selected to correctboth monochromatic aberrations and chromatic variation of aberrationsand focus light to an intermediate image. In the focusing lens group 129a special combination of lenses 130 with low power corrects the systemfor chromatic variation in spherical aberration, coma, and astigmatism.

Design features of the field lens group 127 and the low power group 130are key to the present invention. The zooming tube lens 139 combinedwith the catadioptric objective 128 provides many desirable features.Such an all-refractive zooming lens ideally will allow the detectorarray 140 to be stationary during zooming, although the invention is notlimited to this preferred embodiment. Assuming that the catadioptricobjective system 128 does not also have any zooming function, there aretwo design possibilities open to the zooming tube lens system 139.

First, the zooming section 139 can be all the same refractive material,such as fused silica, and it must be designed so that primarylongitudinal and primary lateral color do not change during zooming.These primary chromatic aberrations do not have to be corrected to zero,and cannot be if only one glass type is used, but they have to bestationary, which is possible. Then the design of the catadioptricobjective 128 must be modified to compensate for these uncorrected butstationary chromatic aberrations of the zooming tube lens. This can bedone, but a solution is needed with good image quality. Despite thelimited image quality, this design possibility is very desirable sincethe whole combined microscope system is a single material, i.e., fusedsilica, except for the calcium fluoride or a diffractive surface in theachromatized Offner-type field lens.

Second, the zooming tube lens group 139 can be corrected for aberrationsindependently of the catadioptric objective 128. This requires the useof at least two refractive materials with different dispersions, such asfused silica and calcium fluoride, or diffractive surfaces.Unfortunately, the result is a tube lens system that, because ofunavoidable higher-order residuals of longitudinal and lateral colorover the entire zoom range, is not capable of high performance over avery broad UV spectral region. Compromises must then be made in the formof reducing the spectral range, the numerical aperture, the field sizeof the combined system, or some combination of these compromises. Theresult is that the very high capabilities of the catadioptric objectivecannot be duplicated with an independently corrected zooming tube lens.

The present invention straddles the two situations just described. Thezooming tube lens 139 is first corrected independently of thecatadioptric objective 128, using two refractive materials (such asfused silica and calcium fluoride). Lens 139 is then combined with thecatadioptric objective 128 and then the catadioptric objective ismodified to compensate for the residual higher-order chromaticaberrations of the zooming tube lens system. This is possible because ofthe design features of the field lens group 127 and the low power lensgroup 130 of the catadioptric objective described earlier. The combinedsystem is then optimized with all parameters being varied to achieve thebest performance.

One unique feature of the present invention is the particular details ofthe zooming tube lens. If the higher-order residual chromaticaberrations of this zooming system change during zoom, then thecatadioptric objective cannot exactly compensate for them except at onezoom position. It is easy to design a zooming tube lens system where thelow-order chromatic aberrations do not change during zoom, and arecorrected to zero as well. But it is very difficult to find a zoomingtube lens design where the higher-order chromatic aberration residuals(which are uncorrectable to zero, in that system by itself) do notchange during the zooming.

A tube lens section can be designed such that its higher-order chromaticaberrations do not change by any significant amount during zoom. If thedetector array 140 is allowed to move during zoom, then the designproblem becomes much easier, but that is not nearly as desirable ashaving an image position fixed relative to the rest of the system.

The imaging system of the invention provides a zoom from 36× to 100× andgreater, and integrates objectives, turret, tube lenses (to provide moremagnifications) and zoom optics into one module. The imaging systemreduces optical and mechanical components, improves manufacturabilityand reduces production costs. The imaging system has several performanceadvantages such as: high optical resolution due to deep UV imaging,reduced thin film interference effects due to ultra-broadband light, andincreased light brightness due to integration of ultra-broad spectralrange. The wide range zoom provides continuous magnification change. Thefine zoom reduces aliasing and allows electronic image processing, suchas cell-to-cell subtraction for a repeating image array. By placing anadjustable aperture in the aperture stop of the microscope system onecan adjust the NA and obtain the desired optical resolution and depth offocus. The invention is a flexible system with an adjustable wavelength,an adjustable bandwidth, an adjustable magnification, and an adjustablenumerical aperture.

There are three possible embodiments of zoom lenses. The firstembodiment provides linear zoom motion with a fixed detector arrayposition. The second embodiment provides linear zoom motion with amoving detector array position. The third embodiment, in addition tozoom lenses, utilizes folding mirrors to reduce the physical length ofthe imaging system and fix the detector array position.

The first embodiment of zoom lenses provides linear zoom motion with afixed detector array position. FIG. 5 shows the 36× zoom arrangement ofthe lenses, the 64× zoom arrangement of the lenses and the 100× zoomarrangement of the lenses. The detector array 140 (not shown) is fixed.The zooming tube lens design 141 is comprised of two moving lens groups142 and 143. The beam splitter is not shown in this and later figuresfor the purpose of clarity. The following table lists the surfaces shownin FIG. 5, where the surface numbering begins at "0" for the final imagecounting towards the object being inspected.

Lens Data for the First Embodiment 0.90 N.A., fixed detector, 36×-100×zoom, 1.0 mm field size

    ______________________________________                                        Surface  Radius    Thickness     Glass                                        ______________________________________                                        0        --        30.000000  36X  Air                                                           152.396279 64X                                                                318.839746 100X                                            1        -46.843442                                                                              4.000000        Calcium fluoride                           2        67.017379 0.999804        Air                                        3        122.003494                                                                              7.000000        Silica                                     4        -34.944144                                                                              4.496612        Air                                        5        -42.883889                                                                              4.000000        Calcium fluoride                           6        -1.5857e+03                                                                             339.659737 36X  Air                                                           298.114540 64X                                                                279.997392 100X                                            7        -657.423731                                                                             9.000000        Calcium fluoride                           8        -67.124645                                                                              0.999689        Air                                        9        -70.484550                                                                              6.000000        Silica                                     10       102.732012                                                                              28.382549       Air                                        11       170.942101                                                                              13.000000       Calcium fluoride                           12       -126.768482                                                                             274.177371 36X  Air                                                           193.326289 64X                                                                44.999970  100X                                            13       103.846671                                                                              5.000000        Silica                                     14       57.151413 3.500000        Air                                        15       113.406488                                                                              7.000000        Silica                                     16       -149.254887                                                                             58.301706       Air                                        17       41.730749 14.904897       Silica                                     18       17.375347 11.364798       Air                                        19       -22.828011                                                                              5.892666        Silica                                     20       -57.773872                                                                              1.000000        Air                                        21       174.740180                                                                              7.000000        Silica                                     22       -48.056749                                                                              4.000000        Air                                        23       24.023380 11.500000       Silica                                     24       -1.0394e+03                                                                             4.198255        Air                                        25       -43.531092                                                                              5.000000        Silica                                     26       -197.030499                                                                             1.000000        Air                                        27       45.618003 29.827305       Silica                                     28       -81.744432                                                                              1.662262        Air                                        29       17.258988 4.000000        Calcium fluoride                           30       -31.010978                                                                              0.315372        Air                                        31       -24.055515                                                                              2.000000        Silica                                     32       5.602559  0.020000        Air                                        33       5.602559  8.318486        Calcium fluoride                           34       -24.871116                                                                              7.710304        Air                                        35       --        8.328925        Air                                        Aperture Stop                                                                 36       85.000000 11.000000       Silica                                     37       70.542512 29.938531       Air                                        38       1.6514e+03                                                                              10.000000       Silica                                     39       Infinity  -10.000000      Reflect                                    40       1.6514e+03                                                                              -29.938531      Air                                        41       70.542512 -11.000000      Silica                                     42       85.000000 -8.328925       Air                                        43       74.648515 8.328925        Reflect                                    44       85.000000 11.000000       Silica                                     45       70.542512 29.938531       Air                                        46       1.6514e+03                                                                              10.000000       Silica                                     47       Infinity  1.500000        Air                                        ______________________________________                                    

The second embodiment of zoom lenses provides linear zoom motion with amoving detector array position and FIG. 6 shows the 36× zoom arrangementof the lenses, the 64× zoom arrangement of the lenses and the 100× zoomarrangement of the lenses. The following table lists the surfaces shownin FIG. 6, where the surface numbering begins at "0" for the final imageincrementing by 1 towards the object being inspected.

Lens Data for the Second Embodiment 0.90 N.A., moving detector, 36× to100× zoom, 1.0 mm field size

    ______________________________________                                        SURFACE  RADIUS    THICKNESS     GLASS                                        ______________________________________                                        0        Infinity  110.004950 36X  Air                                                           405.371660 64X                                                                785.131189 100X                                            1        73.156621 5.000000        Calcium fluoride                           2        -609.638437                                                                             18.230155       Air                                        3        -30.303090                                                                              3.500000        Calcium fluoride                           4        44.361656 4.000000        Air                                        5        -51.318999                                                                              7.765282        Silica                                     6        -23.231195                                                                              1.564401        Air                                        7        -119.756315                                                                             4.000000        Calcium fluoride                           8        40.002701 12.019418       Air                                        9        54.594789 10.000000       Calcium fluoride                           10       -28.923744                                                                              0.100000        Air                                        11       -29.957411                                                                              5.000000        Silica                                     12       -156.281481                                                                             202.434836 36 X Air                                                           108.230318 64X                                                                64.650627  100X                                            13       188.664770                                                                              4.500000        Silica                                     14       56.034008 3.500000        Air                                        15       214.395300                                                                              6.000000        Silica                                     16       -79.842174                                                                              62.685096       Air                                        17       29.721624 10.000000       Silica                                     18       18.529920 11.406390       Air                                        19       -23.406055                                                                              5.864347        Silica                                     20       -46.076628                                                                              1.000000        Air                                        21       94.310969 7.000000        Silica                                     22       -75.041727                                                                              4.000000        Air                                        23       23.509091 11.500000       Silica                                     Aperture Stop                                                                 24       -399.710365                                                                             4.516455        Air                                        25       -42.987793                                                                              10.000000       Silica                                     26       -217.407455                                                                             12.083912       Air                                        27       24.940148 10.000000       Calcium fluoride                           28       -177.604306                                                                             0.100000        Air                                        29       24.508018 10.000000       Calcium fluoride                           30       -54.909641                                                                              0.664880        Air                                        31       -16.389836                                                                              2.000000        Silica                                     32       4.296836  0.020000        Air                                        33       4.296836  3.000000        Calcium fluoride                           34       -14.014264                                                                              7.000000        Air                                        35       --        11.160093       --                                         Internal image                                                                36       102.631452                                                                              11.000000       Silica                                     37       84.741293 27.845569       Air                                        38       1.1470e+03                                                                              10.000000       Silica                                     39       Infinity  -10.000000      Reflect                                    40       1.1470e+03                                                                              -27.845569      Air                                        41       84.741293 -11.000000      Silica                                     42       102.631452                                                                              -11.160093      Air                                        43       75.033466 11.160093       Reflect                                    44       102.631452                                                                              11.000000       Silica                                     45       84.741293 27.845569       Air                                        46       1.1470e+03                                                                              10.000000       Silica                                     47       Infinity  1.500000        Air                                        ______________________________________                                    

The third embodiment of zoom lenses provides linear zoom motion with afixed sensor position by using the same lens design as the secondembodiment and incorporating a "trombone" system of reflective elementsso that the detector array does not move. FIG. 7 shows the 36× zoomarrangement of the lenses and reflective elements, the 64× zoomarrangement of the lenses and reflective elements and the 100× zoomarrangement of the lenses and reflective elements. The folding mirrorgroup 144 is the "trombone" system of reflective elements. This foldingmirror arrangement is just one example. Many other arrangements arepossible, such as, using a different number of reflective elements.

Module Transfer Function curves (not shown) indicate that the FIG. 7embodiment is essentially perfect at 64× and 100×, and is good at 36×.Zooming is done by moving a group of 6 lenses, as a unit, and alsomoving the arm of the trombone slide. Since the trombone motion onlyaffects focus and the f# speed at location is very slow, the accuracy ofthis motion could be very loose. One advantage of the tromboneembodiment is that it significantly shortens the system. Anotheradvantage is that there is only one zoom motion that involves active(non-flat) optical elements. And the other zoom motion, with thetrombone slide, is insensitive to errors.

FIG. 8 is a schematic side view of a catadioptric imaging system with azoom in an application for the inspection of semiconductor wafers.Platform 80 holds a wafer 82 that is composed of several integratedcircuit dice 84. The catadioptric objective 86 transfers the light raybundle 88 to the zooming tube lens 90 which produces an adjustable imagereceived by the detector 92. The detector 92 converts the image tobinary coded data and transfers the data over cable 94 to data processor96.

The exemplary embodiments described herein are for purposes ofillustration and are not intended to be limiting. Therefore, thoseskilled in the art will recognize that other embodiments could bepracticed without departing from the scope and spirit of the claims setforth below.

We claim:
 1. A high numerical aperture, broad spectral regioncatadioptric optical system comprising:a tube lens section which canzoom or change magnification without changing its higher-order chromaticaberrations over a plurality of wavelengths, including at least onewavelength in the UV range; and a non-zooming high numerical aperturecatadioptric objective lens section.
 2. A system as in claim 1 whereinsaid lens sections use fused silica and calcium fluoride.
 3. A system asin claim 1 further comprising a detector array which does not moveduring zooming or a change in magnification of said tube lens section.4. A system as in claim 1 wherein said objective lens section comprisesan achromatized field lens group which eliminates residual chromaticaberrations and compensates said tube lens section for higher-orderchromatic aberrations, and wherein the combination of said lens sectionscorrects for chromatic variations in spherical aberration, coma, andastigmatism.
 5. A high numerical aperture, broad spectral regioncatadioptric optical system as described in claim 1 wherein said tubelens group which can zoom or change magnification without substantiallychanging its higher-order chromatic aberrations.
 6. A high numericalaperture, broad spectral region catadioptric optical system comprising:afocusing lens group including a plurality of lens elements, with lenssurfaces thereof disposed at first predetermined positions along anoptical path of the system and having curvatures and said positionsselected to focus ultraviolet light at an intermediate image within thesystem, and simultaneously to also provide in combination with the restof the system, high levels of correction of both image aberrations andchromatic variation or aberrations over a wavelength band including atleast one wavelength in the UV range; a field lens group with a netpositive power aligned along said optical path proximate to saidintermediate image, the field lens group including a plurality of lenselements with different dispersions, with lens surfaces disposed atsecond predetermined positions and having curvatures selected to providesubstantial correction of chromatic aberrations including at leastsecondary longitudinal color and primary and-secondary lateral color ofthe system over said wavelength band; a catadioptric relay group,including a combination of at least two reflective surfaces and at leastone refractive surface disposed at third predetermined positions andhaving curvatures selected to form a real image of said intermediateimage, such that, in combination with said focusing lens group, primarylongitudinal color of the system is substantially corrected over saidwavelength band; and a zooming tube lens group which can zoom or changemagnification without changing its higher-order chromatic aberrations,and with lens surfaces thereof disposed at fourth predeterminedpositions along an optical path of the system, wherein at least one ofthe non-zooming groups of the high numerical aperture catadioptricoptical system substantially compensates over said wavelength band foruncorrected, but stationary higher-order chromatic aberration residualsof the zooming tube lens group.
 7. A high numerical aperture, broadspectral region catadioptric optical system as described in claim 6wherein said tube lens group can zoom or change magnification withoutsubstantially changing its higher-order chromatic aberrations.
 8. A highnumerical aperture, broad spectral region catadiptric optical system asdescribed in claim 6:wherein said field lens group includes a pluralityof lens elements formed from at least two different refractive materialswith different dispersions.
 9. A high numerical aperture, broad spectralregion catadioptric optical system comprising:a focusing lens groupincluding a plurality of lens elements, with refractive surfaces havingcurvatures and positions selected to focus ultraviolet light at anintermediate image within the system, and simultaneously to also providein combination with the rest of the system, high levels of correction ofboth image aberrations and chromatic variation of aberrations over awavelength band including at least one wavelength in the UV range; afield lens group with a net positive power aligned along said opticalpath proximate to said intermediate image, the field lens groupincluding a plurality of lens elements, with refractive surfaces havingcurvatures selected to provide substantial correction of chromaticaberrations including at least secondary longitudinal color and primaryand secondary lateral color of the system over said wavelength band; acatadioptric relay group, including a combination of at least tworeflective surfaces and at least one refractive surface havingcurvatures selected to form a real image of said intermediate image,such that, in combination with said focusing lens group, primarylongitudinal color of the system is substantially corrected over saidwavelength band; and a tube lens group which can zoom or changemagnification without changing its higher-order chromatic aberrations,and with refractive surfaces, wherein at least one of the non-zoominggroups of the high numerical aperture catadioptric optical systemsubstantially compensates over said wavelength band for uncorrected, butstationary higher-order chromatic aberration residuals of the zoomingtube lens group.
 10. A high numerical aperture, broad spectral regioncatadioptric optical system as described in claim 9 wherein said tubelens group is an all-refractive zooming tube lens group which can zoomor change magnification without changing its higher-order chromaticaberrations.
 11. A high resolution, broadband UV imaging systemcomprising:a detector array which can receive an image over a range ofultraviolet wavelengths; a broadband UV radiation source providing aultraviolet wavelength band; and a catadioptric optical systemcomprising:a focusing lens group including a plurality of lens elements,with refractive surfaces having curvatures and positions selected tofocus ultraviolet light at an intermediate image within the system, andsimultaneously to also provide in combination with the rest of thesystem, high levels of correction of both image aberrations andchromatic variation of aberrations over a wavelength band including onewavelength in the UV range, a field lens group proximate to saidintermediate image, the field lens group including a plurality of lenselements with refractive surfaces having curvatures selected to providesubstantial correction of chromatic aberrations including at leastsecondary longitudinal color and primary and secondary lateral color ofthe system over said wavelength band, a catadioptric relay group,including a combination of at least two reflective surfaces and at leastone refractive surface having curvatures selected to form a real imageof said intermediate image, such that, in combination with said focusinglens group, primary longitudinal color of the system is substantiallycorrected over said wavelength band, and a zooming tube lens group whichcan zoom or change magnification without changing its higher-orderchromatic aberrations, and with a plurality of refractive surfaces,wherein at least one of the non-zooming groups of the high numericalaperture catadioptric optical system substantially compensates over saidwavelength band for uncorrected, but stationary higher-order chromaticaberration residuals of the zooming tube lens group.
 12. A system as inclaim 11 wherein said detector array remains stationary during zoomingor a change in magnification.
 13. A system as in claim 11 wherein saidcatadioptric optical system includes compensation means forachromatizing a field lens and substantially eliminating residualchromatic aberrations and thereby substantially compensate said zoomingtube lens group for higher-order chromatic aberrations, and wherein thecombination of said lens groups substantially corrects for chromaticvariations in spherical aberration, coma, and astigmatism over saidwavelength band.
 14. A high numerical aperture, broad spectral regioncatadioptric optical system comprising:a focusing lens group including aplurality of lens elements, with refractive surfaces thereof disposed tofocus ultraviolet light within the system, and simultaneously to alsoprovide in combination with the rest of the system, high levels ofcorrection of both image aberrations and chromatic variation ofaberrations over a wavelength band including at least one wavelength inthe UV range; a field lens group with a net positive power, the fieldlens group including a plurality of lens elements, with refractivesurfaces having curvatures selected to provide substantial correction ofchromatic aberrations including at least secondary longitudinal colorand primary and secondary lateral color of the system over saidwavelength band; a zooming tube lens section which can zoom or changemagnification without substantially changing its higher-order chromaticaberrations; and a non-zooming catadioptric objective lens section whichprovides means for substantially compensating for uncorrected, butstationary higher-order chromatic aberration residuals of said zoomingtube lens section.
 15. A system as in claim 14 wherein said catadioptricobjective lens section comprises compensation means for achromatizing afield lens and for substantially eliminating residual chromaticaberrations and thereby substantially compensate said tube lens sectionfor higher-order chromatic aberrations, and wherein the combination ofsaid lens sections substantially corrects for chromatic variations inspherical aberration, coma, and astigmatism over said wavelength band.16. A system as in claim 14 wherein at least one of said lenses in thefield lens group comprises a lens made of fused silica.
 17. A system asin claim 14 wherein at least one of said lenses in the field lens groupcomprises a lens made of calcium fluoride.
 18. A high numericalaperture, broad spectral region catadioptric optical system as describedin claim 14 further comprising an all-refractive zooming tube lens groupwhich can zoom or change magnification without substantially changingits higher-order chromatic aberrations.
 19. A high numerical aperture,broad spectral region catadioptric optical system as described in claim14 further comprising a zooming tube lens group with at least onediffractive lens.
 20. A method for constructing a high numericalaperture, broad spectral region catadioptric optical system comprisingthe steps of:providing a focusing lens group including a plurality oflens elements, with refractive surfaces thereof disposed at firstpredetermined positions along an optical path of the system and havingcurvatures and said positions selected to focus ultraviolet light at anintermediate image within the system, and simultaneously to also providein combination with the rest of the system, high levels of correction ofboth image aberrations and chromatic variation of aberrations over awavelength band including at least one wavelength in the UV range;providing a field lens group with a net positive power aligned alongsaid optical path proximate to said intermediate image, the field lensgroup including a plurality of lens elements formed from at least twodifferent refractive materials with different dispersions, withrefractive surfaces of the lens elements of the field lens groupdisposed at second predetermined positions and having curvaturesselected to provide substantial correction of chromatic aberrationsincluding at least secondary longitudinal color and primary andsecondary lateral color of the system over said wavelength band; forminga real image with a catadioptric relay group, including a combination ofat least two reflective surfaces and at least one refractive surfacedisposed at third predetermined positions and having curvatures selectedto form a real image of said intermediate image, such that, incombination with said focusing lens group, primary longitudinal color ofthe system is substantially corrected over said wavelength band; andzooming with a zooming tube lens group which can zoom or changemagnification without changing its higher-order chromatic aberrations,and with lens surfaces thereof disposed at fourth predeterminedpositions along an optical path of the system, wherein at least one ofthe non-zooming groups of the high numerical aperture catadioptricoptical system substantially compensates over said wavelength band foruncorrected, but stationary higher-order chromatic aberration residualsof the zooming tube lens group.
 21. A method for constructing a highnumerical aperture, broad spectral region catadioptric optical system asin claim 20 further comprising the step of:constructing a catadioptricobjective lens section comprising compensation means for achromatizing afield lens and for substantially eliminating residual chromaticaberrations and thereby substantially compensate said tube lens sectionfor higher-order chromatic aberrations, and wherein the combination ofsaid lens sections substantially corrects for chromatic variations inspherical aberration, coma, and astigmatism over said wavelength band.22. A method of imaging an object with a high numerical aperture, broadspectral region catadioptric optical system comprising:zooming with azooming tube lens group which can zoom or change magnification withoutchanging at least a portion of its chromatic aberrations; and imagingsaid object with a non-zooming high numerical aperture catadioptricobjective lens section optimized for imaging in the UV spectral regionwhich substantially compensates for uncorrected, but stationaryhigher-order chromatic aberration residuals of the zooming tube lensgroup.
 23. A high numerical aperture, broad spectral region catadioptricoptical system comprising:a zooming tube lens group which can zoom orchange magnification without changing at least a portion of itschromatic aberrations; and a non-zooming high numerical aperturecatadioptric objective lens section optimized for imaging in the UVspectral region which substantially compensates for uncorrected, butstationary higher-order chromatic aberration residuals of the zoomingtube lens group.